1. Field of the Invention
The present invention relates in general to a controller for controlling a motor operated actuator device, such as a pump device constituting a part of a hydraulically operated braking system, which is installed on a vehicle.
2. Discussion of Related Art
On a vehicle, there are installed various kinds of motor operated actuator devices which are operated by respective motors. Each of the actuator devices, during its activation, generates operating noise and vibration which disturb tranquility or silence in the vehicle. That is, the noise and vibration, when propagated to an occupant of the vehicle, could deteriorate comfort in the vehicle such as feeling in driving the vehicle. In this respect, it is considered to be desirable that generations of the noise and vibration perceivable to the vehicle occupant are restrained.
As an example of technique for reducing the noise and vibration generated by the actuator device, JP-A-H08-127331 (publication of unexamined Japanese Patent Application laid open in 1996) discloses a technique related to control of a pump device of a hydraulically operated braking system. The disclosed technique is directed to control of the pump device on the basis of a running velocity of the vehicle and an operating state of a braking operating member of the braking system, in such a manner that reduces the number of revolutions of a motor of the pump device and the operation time of the pump device, for the purpose of reducing a load applied to the pump device. The reduction in the load applied to the pump device could lead to reduction in generation of the operating noise and vibration. However, the silence and comfort in the vehicle can not be satisfactorily maintained by simply limiting or reducing the output and operation time of the pump motor. This is because a wave such as the noise and vibration is given a proper characteristic with respect to its intensity, which is dependent on factors or phenomena such as resonance occurring in a propagation path between the actuator device (as a wave source) and the occupant of the vehicle.